Ball mill linings and grinding body charges



Aug. 6, ,1957 o; P. FRANKERT BALL MILL LININGS AND GRINDING BODY CHARGESFiled May 10, 1955 2 Sheets-Sheet l 2 FIG/l if PRIOR ART' FIG.-

j 4 ATTORNEY;

6, 1957 o. P. FRANKERT I 2,801,804

BALL MILL LININGS AND GRINDING BODY CHARGES Filed May 10, 1955 2Sheets-Sheet 2 FIG;

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ATTORNEYS United States Patent BALL MILL LININGSi AND GRINDING BODYCHARGES Otto Peder Frankert, Copenhagen, Denmark, nssignor to F. L.Smid'th & C03, New York, N. Y., a corporation of New Jersey 1Application May 10, 1955, Serial No. 507,218

4 Claims. (Cl. 241-183) This invention relates to grinding mills ofthetube and ball types and is concerned more particularly with a mill ofthe kind stated, which is provided with a novel lining constructed toeffect a desired distributionof the grinding bodies and so formed as tohave a long life.

Tube and ball mills have heretofore been provided with linings made upof plates having spaced projections, which act to distribute thegrinding bodies within the grinding chamber andmay be ribs of a widthsmaller than the width of the spaces between adjacent ribs. The ribshave the form of sections of a helix and the platesare so mounted thatthe helices formed by the ribs are of a hand the same as the directionof rotation of the mill shell, when the latter is viewed from the inletend. The projections are spaced sufficiently to permit the largergrinding bodies to enter the depressions between them and, in theoperation of the mill, the projections lift the grinding bodies and thenrelease them with such action chiefly affecting the grinding bodies ofthe larger sizes. As the projections are helical and thus lie at anangle to the generatrices of the cylindrical shell, the proje'ctionsacts to advance the lifted grinding bodies lengthwise of the mill axisand, with the helices of the hand described, the movement of the largergrinding bodies is toward the inlet end of the mill, through which thematerial to be ground is fed. Such distribution of the grinding bodieswithin the mill is desirable and the grinding action in a mill equippedwith a liner as described is superior to that in mills, in which theliner performs no distributing function. However, such projectionsnarrower than the spaces between them wear down rapidly during theoperation of the mill with the result that the distributing effect islost or the liner must be replaced to maintain the effect.

Mills as heretofore constructed have commonly been subdivided into aseries of grinding chambers or compartments separated from one anotherby grids, which retain the grinding bodies within the severalcompartments while permitting the sufficiently ground material to passfrom one compartment to the next. The grinding bodies within therespective compartments are about uniform in size, so that bodies ofdifferent size may be introduced into the several compartments, and keptin those compartments by the grids. However, the grids tend to becomeclogged by the material being ground or by the grinding bodies and suchclogging reduces the efficiency of the mill and may necessitate itsbeing stopped, so that the grids can be cleaned.

The present invention is directed to the provision of a tube or ballmill having a shell lining, which causes proper distribution of thegrinding bodies, but is so constructed as to have a long life. The useof the new lining makes possible the sorting or distribution accordingto size of a charge of grinding bodies varying widely in size, as, forexample, a charge, in which the bodies forming at least by weight of thecharge are all of a diameter. at least 75% greater than the averagediameter at the bodies forming another fraction of the charge 2,801,804Patented Aug. 6, 1957 The lining of the invention is formed with spaced,

projections on its inner surface, which have an average width at leasttwice and preferably more than twice the average width of the spacesbetween them. The projections have the shape of sections of helices of ahand opposite to the direction of rotation of the mill viewed from theinlet end, and are so close together and of such radial depth thatgrinding bodies making up at least 10% by weight of the charge are toolarge to penetrate to the bottom of the spaces between the projections.As a result of forming the lining as described, the smallest grindingbodies enter the spaces between the projections and slide through thespaces during rotation of the mill, so that they are conveyed axially ofthe mill toward the outlet end. At the same time, the projections are ofsuch width that the lining undergoes almost uniform wear over its entiresurface.

For a better understanding of the invention, reference may be made tothe accompanying drawing, in which Fig. l is a diagrammatic developedview of a section of a mill lining of the prior art;

Fig. 2 is a sectional view on the line 2-4 of Fig. I;

Fig. 3 is a diagrammatic developed view of a section of a mill lining ofthe invention;

Fig. 4 is a sectional view on the line 4-4 of Fig. 3;

Fig. 5' is a view similar to Fig. 3 showing. a modified construction;

Fig. 6 is' a sectional view on the line 66 of Fig. 5;

Fig- 7 is a view similar to Fig. 3 showing a second modifiedconstruction;

Fig. 8 is a sectional view on the line h-8 of Fig. 7;

Fig. 9 is a view in side elevation of a grinding mill with parts brokenaway to show the installation of the liner of the invention;

Fig. 10 is a view of the inlet end of the mill of Fig. 9 with aportionof the head broken away; and

Figs. 11, 12, and 13' are diagrammatic developed views showing threedifferent mill linings embodying the invention.

The prior mill lining, of which a portion is shown in Figs. 1 and 2, ismade up of a plurality of plates 11, which are of arcu'ate form and aremounted on the inner face of the shell 12. The plates are formed ontheir exposed inner faces with spaced helical ribs 13, which are of lesswidth than the depressions 14 between them. Ordinarily, the plates areso mounted that the ribs on one plate are aligned with those on theadjacent plates, so that the lining is provided with continuous helicalribs extending from one end of the shell to the other and separated bycontinuous depressions. The helices formed by the ribs are of a hand thesame as the direc; tion of rotation of the shell when viewed from theinlet end, as indicated by the arrow.

In the operation of the mill equipped with the prior lining, the largergrinding bodies enter the depressions 14 and are lifted. by theprojections and also advanced axially of the mill. As a result of thisaction, the charge of grinding bodies in the mill is distributedaccording to the size of the individual bodies and the larger grindingbodies accumulate at the inlet end of the mill and the distributingeffect is soon lost or can be maintained D y by replatiemg nt pf the Thelining of the invention in the form illustrated in Fig. 3 is made up ofarcuate plates 15' formed with depressions 16 separated by projectionsor lands 17. The projections are wide in relation to the depressions andare preferably more than twice as wide as the depressions. Thedepressions may be of V-section, as shown, and the depth of theprojections measured from their top to the bottom of a depression issuch that a large grinding body B cannot penetrate to the bottom of adepression, while a small grinding body B may do so. The projections aresections of helices of a pitch between 30 and 60 with a pitch of 45preferred and the plates are so mounted in the shell that theprojections form continuous helical channels from one end of the shellto the other, although the helices may be interrupted. The helices areof a hand opposite to the direction of rotation of the shell viewed fromthe inlet end. Since the large grinding bodies cannot penetrate to thebottom of the depressions, the latter have little lifting efiect on suchbodies, but the small grinding bodies entering the depressions are movedlengthwise of the mill toward the outlet end thereof .as the millrotates. The movement of the smaller grinding bodies toward the milloutlet results in the larger bodies accumulating near the the inlet, asis desirable. The distributing action of the new lining is thus the sameas that of the prior lining of Fig. 1, but the new lining has a muchgreater life than the prior one, since the wear on the new lining istaken by the relatively wide projections. The wear on the new lining ismore uniform than that on the prior lining and the new lining willperform its distributing function throughout substantially the entirelife of the lining.

The modified form of the lining shown in Figs. and 6 is especiallysuitable for use in grinding chambers containing a charge of smallcylindrical grinding bodies and is made up of relatively narrowdepressions 20 separated by relatively wide bars 21 of helical shape.Each depression is a row of long narrow holes 22 extending through theplates to the inner face of the mill shell and separated by bridgepieces 2.3 connecting adjacent bars and lying against the mill shellwith the tops of the bridge pieces below the tops of the bars. When sucha lining is installed, the holes 22 may be filled with the material,such as cement mortar, which is less resistant to wear than the bars 21.The width of the depressions 20 is such as to allow only the smallestgrinding bodies to enter them and thereby subject the sides of the barsand the filling material in the holes to wear.

The lining shown in Figs. 5 and 6 may be provided, if desired, byreplacing the plates by bars corresponding in shape and size to the bars21 and mounted within the shell'in spaced relation. If desired, platesof the height of bridge pieces 23 may be mounted in the spaces betweenthe bars.

The modified form of the new liner shown in Figs. 7 and 8 is made up ofplates formed with frusto-conical projections 24 lying in helical rows25. Adjacent rows are spaced apart and the spaces form depressions 26,which are of varying width. The average width of the depressions 26 isless than the average diameter of the projections, so that thedepressions perform the same functions as the depressions 16 in theconstruction shown in Fig. 3.

The liner of the invention may be used in tube or ball mills, one ofwhich is diametrically shown in Figs. 9 and as comprising a cylindricalshell 27 with heads 28 at its opposite ends. One head is provided withan inlet 29 for introduction of the material to be ground and the otherwith an outlet 3% for discharge of ground material. The direction ofrotation of the mill, when viewed from the inlet end, is clockwise andthe grooves 16 in the liner plates thus tend to advance the smallgrinding bodies toward the outlet end of the mill. As

a result, the larger grinding bodies accumulate near the inlet, which isthe desired distribution of the grinding bodies.

The use of the new lining in compartment mills is illustrateddiagrammatically in Figs. 11, 12, and 13. The mill shown in Fig. 11 is atypical tube mill having a shell 31 with an inlet 32 at one end and anoutlet 33 at the other. The interior of the mill is divided into twochambers or compartments by a grid 34, which may have openings about 4mm. in diameter, and another grid 35 is disposed near the outlet 33. Thefirst compartment 36 is provided with a lining 37 made up of plates asshown in Figs. 3 and 4, while the second compartment 38 is provided witha lining 39 made up of plates as shown in Figs. 5 and 6. Near the grid35, the lining 39 is formed with a zone 39a, in which the plates are somounted that the depressions indicated by the lines 40 are helical andof a hand opposite to that of the helical depressions elsewhere incompartments 36, 38 and the same as the direction of rotation of themill viewed from the inlet end. The depressions in the zone 39a act tomove the smallest grinding bodies away from the grid 35 so as to avoidclogging of the openings in the grid by the worn bodies.

The mill shown in Fig. 11 is intended for grinding materials, which aresoft and easily ground. The grinding bodies in compartment 36 may,accordingly, be balls varying from 30 mm. to 100 mm. in diameter, whilethe bodies in compartment 38 may be cylindrical pebbles of a sizevarying between 8 mm. and 22 mm.

The mill shown in Fig. 12 is generally similar to that shown in Fig. 11and includes a shell 41 with an inlet 42 at one end and an outlet 43 atthe other. The interior of the mill is divided into two compartments bya grid 44 and another grid 45 is disposed near the outlet 43. The firstcompartment 46 is shorter and the second compartment 47 is longer thanthe corresponding compartments in the millof Fig. 11. The mill of Fig.12 is intended for grinding relatively hard materials and the charge ofgrinding bodies in compartment 66 may consist of steel balls ofdiameters varying from mm. to mm., while the charge in compartment 47may consist of balls of diameters varying from 30 mm. to 40 mm. andcylindrical pebbles of a size varying between 8 mm. and 2.2 mm. The grid44 passes only pieces of material less than about 4- mm. in diameter andthe greater length of compartment 47 insures that the materials willremain in that compartment a sufficient length of time for grinding tothe desired fineness. The zone 47a corresponds to zone 39:: and, in it,the liner plates are so disposed that the helical depressions are of ahand the same as the direction of rotation of the mill viewed from theinlet end.

The mill shown in Fig. 13 is of the single compartment type andcomprises a shell 48 with an inlet 49, an outlet 50, and a grid 51 nearthe outlet. The lining 52 is formed of plates as shown in Figs. 3 and 4except for a zone 52a near the outlet, in which the plates are of thetype shown in Figs. 5 and 6 and are so mounted that the depressionsindicated by the lines 5'3 are of a hand the same as the direction ofrotation of the mill viewed from the inlet end. The mill is intended forgrinding coal and may have a charge of grinding bodies consisting ofsteel balls of diameters varying between 30 mm. and 50 mm. andcylindrical pebbles of sizes varying between 8 mm. and

22 mm. By causing the mill to be air-swept to withdraw the finishedground material, it is possible to eliminate grid 51 and therebyincrease the mill efficiency.

I claim:

1. A grinding mill, which comprises a cylindrical shell containing acharge of grinding bodies of varying sizes and having an inlet at oneend and an outlet at the other, and a lining within the shell havingprojections on its inner surface separated by depressions and of anaverage width greater than the average width of the depressions, theprojections beingbars having the shape of sections.

of helices of a hand opposite to the direction of rotation of the shellviewed from the inlet end and the depressions containing bridge piecesconnecting the bars and lying in spaced relation.

2. The mill of claim 1, in which the width of the projections is atleast twice the width of the depressions.

3. The mill of claim 1, in which the depressions are filled at least inpart by a material softer than that of the lining.

4. The mill of claim 1, in which the lining is made of plates, thedepressions are formed by holes extending through the plates, and thebridge pieces lie wholly within the holes and against the inner surfaceof the shell.

References Cited in the tile of this patent UNITED STATES PATENTS689,347 Hundeshagen Dec. 17, 1901 6 Barry May 12, 1908 Hardinge Feb.8,1921 Bonnot et al. June 22, 1926 Hardinge May 26, 1931 Fitzgerald Nov.14, 1944 Henricot Ian. 16, 1945 FOREIGN PATENTS Great Britain of 1902Germany Mar. 3, 1902 France Mar. 15, 1926 OTHER REFERENCES Ser. No.312,133, Henricot (A. P. 0.), published May

